This invention pertains to radiation scintillation imaging detection systems, such as radiation scanners and scintillation cameras, and more particularly, to circuitry which may be utilized with imaging detection systems, for reducing data losses of randomly occurring data signals.
In the diagnosis of certain illnesses, radioactive isotopes are frequently administered to the patient. These isotopes have the characteristic of concentrating in certain types of tissue, and the degree of concentration in the tissue is dependent on the type of tissue. For example, Iodine 131 generally collects or concentrates in the tissue of the thyroid gland. Upon detection of the level of radioactive isotope concentration and presentation of this detected information on a suitable readout device, such as an oscillioscope, it is frequently possible to diagnose the condition of the tissue under examination.
One well-known type of device for detecting levels of radiosotope concentration is the scintillation camera. Scintillation cameras generally incorporate a relatively large disc-shaped scintillation crystal which is positioned so that the crystal scintillates upon absorbing gamma-ray energy to thereby provide pulses of light energy. A thallium activated sodium iodide crystal is typically employed to produce scintillations upon being struck by gamma radiation.
A plurality of phototubes are positioned with respect to the crystal so that a light pulse occurring in the crystal is normally detected by several of the phototubes. Each of the detecting phototubes develops an electrical signal in response to the light pulse which is of an amplitude proportional to the intensity of the light energy and the distance between the light pulse and the phototube. The signals developed by the phototubes are then amplified and applied to appropriate electronic circuitry to thereby develop electrical data signals representative of the position, as well as the intensity, of the light pulse or scintillation. One such gamma-ray imaging camera system is disclosed in the above-referenced patent application entitled, Scintillation Camera, which is incorporated herein by reference.
Prior art scintillation cameras of the type described above use a video tape recorder to record data signals representing radiation events. The signals are stored and used in subsequent imaging operations. The video tape recorder can accept data only during each of a plurality of equally spaced time intervals, or "slots."
One problem with such cameras is that information borne by the data signals is often lost when the data signals occur spaced in time at intervals shorter than those separating the time slots of the recorder. In such cases, data occurring too soon after the occurrence of a previous data signal must simply be aborted, and its informational value not used.
On the other hand, when data signals occur with less frequency than that of the recorder time slots, undesirable recorder down time occurs. When the data signals are spaced too far apart, the recorder and its downstream processing circuitry must wait for the occurrence of a new data signal before it can be processed.